CLI option to enable authoring when offline (#2104)

* CLI option to enable authoring when offline

* Update core/service/src/config.rs

Co-Authored-By: arkpar <arkady.paronyan@gmail.com>

substrate/core/service/test/src/lib.rs

@@ -120,6 +120,7 @@ fn node_config<F: ServiceFactory> (
 		rpc_ws: None,
 		telemetry_endpoints: None,
 		default_heap_pages: None,
+		force_authoring: false,
 	}
 }